Malaria

Malaria is a life-threatening parasitic disease transmitted by mosquitoes. The term malaria originates from Medieval Italian, mala aria (bad air) due to its association with swamps. In 1880, scientists discovered the real cause of malaria, a one-cell parasite called plasmodium. Later, they discovered that the parasite is transmitted from person to person through the bite of a female Anopheles mosquito, which requires blood to nurture her eggs.

Today, approximately 40 percent of the world's population—mostly those living in the world's poorest countries—are at risk of malaria. The disease was once more widespread but it was successfully eliminated from many countries with temperate climates during the mid-20th century. Now, malaria is found throughout the tropical and subtropical regions of the world and causes more than 300 million acute illnesses and at least 1 million deaths annually. It is endemic in parts of Asia, Africa, Central and South America, Oceania, and certain Caribbean islands. Malaria, together with human immunodeficiency virus (HIV)/AIDS and tuberculosis, is one of the major public health challenges undermining development in the poorest countries in the world.

Malaria is caused by protozoan parasites of the genus Plasmodium (phylum Apicomplexa). In humans, malaria is caused by P. falciparum, P. malariae, P. ovale, and P. vivax. However, P. falciparum is the most important cause of disease and responsible for about 80 percent of infections and 90 percent of deaths. P. falciparum malaria is most common in Africa, south of the Sahara, accounting in large part for the extremely high mortality in this region.

The malaria parasite enters the human host when an infected Anopheles mosquito takes a blood meal. Inside the human host, the parasite undergoes a series of changes as part of its complex life cycle. Its various stages allow plasmodia to evade the immune system, [Page 1051]infect the liver and red blood cells, and finally develop into a form that is able to infect a mosquito again when it bites an infected person. Inside the mosquito, the parasite matures until it reaches the sexual stage where it can again infect a human host when the mosquito takes its next blood meal, 10 to 14 or more days later.

Malaria symptoms appear about nine to 14 days after the infectious mosquito bite, although this varies with different plasmodium species. It is characterized by extreme exhaustion associated with paroxysms of high fever, sweating, shaking chills, and anemia. If drugs are not available for treatment or the parasites are resistant to them, the infection can progress rapidly to become life threatening. Malaria can kill by infecting and destroying red blood cells (anemia) and by clogging the capillaries that carry blood to the brain (cerebral malaria) or other vital organs.